Quantification of Epigenetic and Genetic 2nd Hits in CDH1 During Hereditary Diffuse Gastric Cancer Syndrome Progression

Abstract

Background & Aims:Hereditary diffuse gastric cancer (HDGC) families carry CDH1 heterozygous germline mutations; their tumors acquire complete CDH1 inactivation through "2nd-hit" mechanisms. Most frequently, this occurs via promoter hypermethylation (epigenetic modification), and less frequently via CDH1 mutations and loss of heterozygosity (LOH). We quantified the different 2nd hits in CDH1 occurring in neoplastic lesions from HDGC patients. Methods: Samples were collected from 16 primary tumors and 12 metastases from 17 patients among 15 HDGC families; CDH1 mutations, LOH, and promoter hypermethylation were analyzed. E-cadherin protein expression and localization were determined by immunohistochemistry. Results: Somatic CDH1 epigenetic and genetic alterations were detected in lesions from 80% of HDGC families and in 75% of all lesions analyzed (21/28). Of the 28 neoplastic lesions analyzed, promoter hypermethylation was found in 32.1%, LOH in 25%, both alterations in 17.9%, and no alterations in 25%. Half of the CDH1 2nd hits in primary tumors were epigenetic modifications, whereas a significantly greater percentage of 2nd hits in metastases were LOH (58.3%; P ‫؍‬ .0274). Different neoplastic lesions from the same patient frequently displayed distinct 2nd-hit mechanisms. Different 2nd-hit mechanisms were also detected in the same tumor sample. Conclusion: The 2nd hit in CDH1 frequently occurs via epigenetic changes in HDGC primary tumors and LOH in metastases. Because of the concomitance and heterogeneity of these alterations in neoplastic lesions and the plasticity of hypermethylated promoters during tumor initiation and progression, drugs targeting only epigenetic alterations might not be effective, particularly in patients with metastatic HDGC.

Histopathological, Molecular, and Genetic Profile of Hereditary Diffuse Gastric Cancer: Current Knowledge and Challenges for the Future

“…In fact, E-cadherin protein expression, detected by IHC can either be lost or maintained, regardless of CDH1 germline mutation and HDGC tumour stage. Similar observations in HDGC invasive carcinomas have been documented in several studies [52,53]. Thus, IHC analysis of E-cadherin in HDGC lesions (early and advanced) is not a good marker to detect CDH1 gene complete inactivation or to predict whether an early lesion will evolve or not to invasive cancer.…”

“…In fact, 50% of primary GC displayed CDH1 epigenetic modifications as a second-hit, whereas in GC metastases the most common second-hit was loss of heterozygosity. Different neoplastic lesions from the same patient frequently displayed different types of second-hits and different types of second-hits were also found within the same tumour sample [50,52,53]. These results demonstrated substantial heterogeneity in the mechanisms that can act as CDH1 second-hits in a single patient.…”

“…Initial reports indicated that the second-hit that inactivates CDH1 in HDGC is most commonly promoter hypermethylation [50,52]. In 2009, Oliveira et al performed a systematic study to establish the frequency of different types of somatic CDH1 second-hits occurring in CDH1-related GC [53]. This study confirmed that promoter hypermethylation was the most frequent second CDH1 hit, identified in 32.1% of the lesions analyzed, whereas loss of heterozygosity was found in 25%, both alterations in 17.9% and no alterations in 25%, when both primary GC and lymph node metastases were analyzed [53].…”

“…In 2009, Oliveira et al performed a systematic study to establish the frequency of different types of somatic CDH1 second-hits occurring in CDH1-related GC [53]. This study confirmed that promoter hypermethylation was the most frequent second CDH1 hit, identified in 32.1% of the lesions analyzed, whereas loss of heterozygosity was found in 25%, both alterations in 17.9% and no alterations in 25%, when both primary GC and lymph node metastases were analyzed [53]. In fact, 50% of primary GC displayed CDH1 epigenetic modifications as a second-hit, whereas in GC metastases the most common second-hit was loss of heterozygosity.…”

“…The appearance of early HDGC lesions, that may or may not evolve to widely invasive carcinomas, is thought to be triggered in the stomach by the somatic inactivation of the remaining CDH1 wild-type allele [50,52,53]. Although it would be conceivable that complete CDH1 gene inactivation leads to complete loss of E-cadherin protein expression, this is not always the case.…”